Composite fabrics are used in a variety of applications such as medical protective garments, surgical drapes, filtration, and house wrap. The composite fabrics used in medical and surgical applications often require sterilization prior to their use. Several sterilization techniques, including gamma radiation, ethylene oxide and steam, are used in the industry. Gamma radiation sterilization is the preferred technique. During exposure to gamma radiation, significant degradation of fabric components can occur, causing the loss of mechanical properties. Therefore, it is desirable that these fabrics are constructed of components that are not significantly affected by the gamma radiation levels used in commercial sterilization processes. These composite fabrics typically comprise at least one fibrous layer to provide textile-like feel and comfort.
Polypropylene fibers are conventionally used for preparing nonwoven fabrics, since polypropylene is capable of thermally bonding over a broad temperature range and polypropylene fiber can be carded into light webs at high speeds. However, exposure to gamma radiation causes considerable deterioration of the mechanical properties of polypropylene. Not only does such deterioration occur immediately after exposure, but the deterioration from that exposure continues over the course of time.
In contrast to polypropylene, polyethylenes generally do not undergo extensive deterioration upon exposure to the dosages of gamma radiation that are employed for sterilizing medical items. Polyethylene fabrics have other favorable attributes, including soft hand, good drape, and heat sealability to polyethylene films. Polyethylene is also widely recognized for its relative chemical inertness in comparison with polyester or nylon fabrics, especially its resistance to acidic or alkaline conditions.
Composite fabrics are described, for example, in U.S. Pat. No. 5,169,712. The preparation of a breathable film based on less than 50% random copolymer of ethylene-propylene, and composite structures containing this film are disclosed. U.S. Pat. No. 5,173,356 describes self-bonded fibrous nonwoven webs and composite products made from these webs. U.S. Pat. No. 4,196,245 discloses a three ply composite made from at least one cover ply, e.g., an apertured polyethylene film, a spunbonded web, or a carded web, and two plies of melt-blown thermoplastic fibers, e.g., polypropylene fibers. U.S. Pat. No. 4,726,976 discloses a composite structure comprising one middle layer of apertured thermoplastic film, e.g., polyethylene film, secured to a top hydrophobic fibrous web and a bottom hydrophilic fibrous web, e.g., nonwoven polypropylene fibrous webs. A composite structure of polyethylene film and polyethylene/polyester sheath/core bicomponent fibers is described in Japanese published patent applications JP 51-24144 and JP 10-69322.
There is still a need for a barrier fabric that is inexpensive to produce, retains its mechanical properties after exposure to gamma radiation, and has a textile-like feel and comfort.